Variable grid leak



March 20, 1928. 1,663,166

| JONES VARIABLE GRID LEAK Filed March 16, 1923 INVENTOR Lesfer L. Jones.4 TTORNE Y8 Patented Mar. 20, 1928.

UNITED STATES LESTER L. JONES, F ORADELL, NEW JERSEY.

VARIA LE GRID LEAK.

Application filed March 16, 1923. Serial No. 625,484. i

This invention relates to the control of thermionic or electron tubes,and more particularly to a grid leak device designed for radio receivingcircuits; and has special reference to the provision of a new-and1mproved variable grid leak.

As is well known, to control the current flowing between the plate andthe filament of a thermionic or electron tube in a radio circuit, thepotential on the grid of the tube relatively to that of'a terminal ofthe filament is controlled by means of the so-called grid leak, thefunction of which is to present a leakage path across a grid condenserto maintain the potential of the grid at some desired value. It is alsoWell known that different circuits require grid leaks of differentvalues, the value being dependent upon the operating characteristics ofa given tube and its use as a detector, amplifier or oscillator, andupon such factors as the design of the apparatus, the type of antennaused, and the ground system employed; and

to meet these varying requirements grid condensers have been combinedwith variable resistances to produce Variable grid leaks which maybeadjusted to suit the different needs of service.

To be adaptable for the different circuits and tubes met with inpractice, it has been found that the range of resistance change of l avariable grid leak should be fairly large,

a variation of from about to 10 megohms having been found a desideratum,if not indeed a requirement, to suit the many different conditionspresented. The adjustment for many circuits and tubes is moreover highlysensitive, and'consequently another desideratum in the design of aserviceable variable grid leak is the capability of permitting smallresistance changes when the grid leak is adjusted-to produce a setting.Furthermore, in View of the fact that circuits and tubes of widelydifferent characteristics and properties may be equally sensitive atwidely different values of leak resistance, it is very desirable toprovide a leak resistance which is uniformly changeable when varied, andone preferably which possesses a straight-line calibration curve. Toprovide a variable grid leak which is characterized by the desired largerange of resistance variation'and a variation over a long adjustmentpath to afford sensitive conness over thelarge range of adjustment is aprime object of my present invention.

In the construction of variable grid leaks, the resistance terminals areconnected to the condenser electrodes or plates, and according to priorcommonly employed designs, the means connecting the condenser andresistor are constructed to provide one or more connecting terminals orbinding posts for the grid leak device, the movable contact arm for theresistor being sometimes employed as one of the connecting means. I havefound that these prior grid leak structures are opento the commonobjection of producing loose contacts, especially after some use, eitherat the connecting terminals or at the dial shaft carrying the contactarm with the result that the adjusted value of leak resistance isvaried, and not only is the adjustmentvitiated, but an undesirable looseconnection in the set is produced. This disadvantage I have foundespecially pronounced-in that type of grid leak construction wherein theresistance element is made up of graphite streaks or lines produced onan insulating surface with the aid of a pencil, the integrity of theelectrical connection between the graphite surface and the connectingterminals and condenser electrodes being diificult to maintain. Toobviate these disadvantages and objections, and to produce a variablegrid leakdevice in which the condenser and resistor units are connectedso as to minimize liability of loose contacts, while at the same timeproviding for ready severability between the condenser and stator units,is another prime desideratum of my present invention.

Another important problem in the design of a variable grid leak is thatof eliminating the troublesome changeable capacitive effects in thecircuit produced by the changing position of the hand or bodyof theoperator in obtaining a setting of the leak. The connection of the gridleak to the high potential side of the grid circuit renders itparticularly difiicult to obtain the desired setting, the largediiferences of potential between the circuit and the operators handproducing relatively large capacitive changes and a consequentunbalancing effect on the circuit. To eliminate this objection mypresent invention further comprehends the provision of a grid leakdevice in which the parts are so electrostatically shielded as to makean adjustment of the same entirely an affected by the hand of theopeartor,

The principal objects of my invention may be said to include, besidesthe provision of a variable grid leak structure having thecharacteristics and capable of producing the results above-mentioned;the further provision of a grid leak structure in which a resistor unitis so combined with a condenser unit as to permit ready detachability ofthe former for purposes of repair and replacement without interferingwith the integrity of the latter; the still further provision of a gridleak device designed so as to be mountable on a support such as a panel;and the provision of a variable grid leak made of a few parts sointer-related as to permit rapid manufacture and ease of assembly toprovide a low cost unit.

To the accomplishment of the foregoing and such other objects as mayhereinafter appear, my invention consists in the elements and theirrelation one to the other, as hereinafter particularly set forth andsought to be defined in the claims; reference being had to theaccompanying drawings wherein: a

Fig. 1 is a side elevational View of my grid leak device showing partsin section and showing the same attached to a support such as a panel, I

Fig. 2 is a rear view of the same with parts broken away, 1

Fig. 3 is a perspective view of the resistance element employed,

Fig; 4 is a development view of the 'peripheral wall or surface of theresistance element,

Fig. 5 is aview showing the assembly of parts of the grid leak device,and

Fig. 6 is a view of the grid leak on a reduced scale the oppositecondenserplates l0 and 11 and an intermediate dielectric plate 12 whichmay comprise a sheet of mica, locked between the two spaced insulatingblocks 13 and 14 carried on a sleeve 15 which may be formed integrallywith a front supporting plate 16, the said sleeve being threaded assit/17 for receiving a lock nut 18, the insulating blocks 13 and 14 andthe condenser elements therebetween being held between the front plateand the lock nut, the sleeve 15 and the nut 18 forming in effect a tiebelt for holding these elements securely in assemprises a resistanceelement formed by pro ducing two concentric lines 19 and 20 composed ofa high resistance material pro duced on the peripheral wall 521 of adisklike member 22 made of an insulating material such as hard rubber orbakelite, the said disk-like member being preferably mounted on anoperating spindle or shaft 23 and secured thereto as by means of the nut24 received by the threaded end 25 of the said spindle. lhe concentricresistance lines 19 and 20 may comprise graphite streaksor linesproduced with the aid of a pencil, and may be made by placing theresistance element in a lathe and applying the point of the pencil tospaced parts'of the peripheral wall 21 to effect two continuous andcircular pencil strokes, after which a portion of the lines so producedmay be erased as at 26 and the lines connected at one end by means ofthe cross stroke 27, two spaced discontinuous lines connected at one endbeing thereby provided as clearly shown in development in Fig. 4 of thedrawings. By the provision of this resistance element, it will beapparent that I am enabled to pro- .vide not only a very largeresistance range such as a range of from about to 1O megohms, but aresistance range extending over a long path, so that when a contactmeans is moved over and relatively to the resistance lines19 and 20, avariation over a long adjustment path to afiord the desired sensitivecontrol is obtained, and that moreover ll am enabled to obtain uniformsensitiveness over the whole path of adjustment, the resistance elementpossessing a substan tially straight-line calibration curve.

As hereinbefore stated, it is a desideratum of the present invention toproduce a variable grid leak in which the condenser and resistor unitare so associated and connected as to produce efiicientcontacts and tominimize the liability of looseness of contacts, while at the same timeproviding for ready severability between the condenser and resistorunits, with the parts so inter-related as to permit of elfectivecapacitive shielding. To "these andother ends, the resistance element ofthe resistor unit is preferably made movable with the contact armstherefor preferably made stationary, the resistance element comprisingto this end the rotatable disk-like member 22 heretofore referred to,the spindle 23 of which is receivable by are journalled within thesleeve 15 of the condenser unit, the said spindle 23 extending throughsaid sleeve and being constructed to receive the operating dial D andthe contact means comprising to thisend the spaced contact arms 28 and29 which are formed preferably integrally with the spaced condenserplates 10 and 11 respectively andproduced from blanks of sheet materialas will be detailed further hereinafter, the said contact arms 28 and 29being so contoured as to provide the spaced contact fingers 28' and 29arranged in overlapping engagement as clearly shown in Figs. 1, 2 and 6of the drawings, and in contacting relation with the spaced resistancelines 19 and 20. Also formed integral with the spaced condenser plates10 and 11, I provide the connecting terminals for the grid leak 30 and31, which terminals may be provided at their outer ends with theapertures 32 and 33 for the reception of connecting conductors. By theprovision of this construction it will be seen that the contact arms areefficiently united to the connecting terminals of the grid leak deviceso as to eliminate the possibility of any looseness of contacttherebetween, these parts being moreover efficiently connectedelectrically to the condenser plates so as to provide the desiredpermanent interconnection between the condenser and resistor units.Moreover, it will be evident that with the provision of this arrangementthe resistance element may be quickly detached from the condenser unit,as when it is desired to repair or replace the same, by simplywithdrawing the disk member 22 and its at tached shaft or spindle 23,this being accomplished without affecting the identity or integrity ofthe contact arms or connecting terminals.

Referring now to Fig. 5 of the drawings, I show the manner of making andassembling the condenser unit and its mounting. For facilitating theprocess of manufacture, the condenser plates and the integral partsthereof are produced from the same blanks,

each of which is apertured as at 34 for re ceiving the supporting sleeve15, the integral contact arms 28 and 29 and the connecting terminals 30and 31 being produced by bending these parts to opposite sides of therespective plates 10 and 11. The plate 11 is further provided with anintegral tab 35 which'is turned down or bent over to be received by anotch 36 in .the insulating block 14:, and the plate 10 is also providedwith a tab 37 which is bent or turned down in the opposite direction tobe received by a notch 38 in the insulating block 13, the condenserplates by this means being locked to the insulating blocks so that allthe condenser arts are secured together in a unit, The insulating block13 is also provided with the recess or notch 39 for receiving thecontact arm 29 and connecting terminal 31, and

with the recess or notch 40 for receiving in position and the wholesecured together by means of the lock nut 18. After assembling thecondenser, the resistance element is then mounted thereon by insertingthe spindle 23 in the supporting sleeve 15.

For housing the condenser and resistor units, and for capacitivelyshielding the same, I rovide a casing 41 which may be connecte to groundin a receiving circuit, and which is desirably secured: to the frontsupporting plate 16 as bymeans of the securing elements 42, the saidcasing being provided, with a plurality of slits 13 at its base throughwhich may project the connecting grid leak terminals 30 and 31. Ifdesired insulating washers or bushings 4A may be provided at "the slits43. For the purpose ofholding the resistance element in position, andfor the further purpose of electrically connectin the shaft or spindle23 to the casing, the ase of the casing is pro-' vided with an inwardlyprojecting portion 45 which engages the end of the shaft 23 as appearsclearly from a consideration of Figs. 1 and 6 of the drawings. By theprovision of the'casing 40 and its connection to the metallic frontplate 16 and to the metallic shaft 23, I provide a complete capacitiveor electrostatic shielding for the grid leak parts so as to make anadjustment of the same entirely unaffected by the hand or body of theoperator. The casing if desired may be made out of an insulatingmaterial, in which event the metallic plate 16 and the spindle 23, beingpositioned between the operators hand and the grid leak parts, act asthe electrostatic shield for the latter.

The method of making and using my variable rid leak will in the main beapparent from t e above detailed description thereof. It will befurthenapparent that I have provided a variable grid leak in which theresistor, and condenser elements are efliciently interrelated with theformer capable of being removed or replaced for repairing the graphitestreaks as for making any other repairs found necessary in practiceWithout necessitat-ing removal of the condenser parts. It will befurther seen that the variable grid leak provided is adaptable for thedifferent circuits and tubes met with in practice, sensitive adjustmentsbeing possible over along range of resistance variation. The resistanceand condenser elements, moreover, may be cheaply produced and assembledwith ease, and are so inter-related as to permit of the desiredelectrostatic shield.

l Vhile l have shown my device in the preferred form, it will be obviousthat many changes and modifications may be made in the structuredisclosed without departing from the spirit of the invention, defined inthe following claims,

I claim: v

1. A new article of manufacture comprising a fixed condenser,connecting-terminals integral with opposite plates of said condenser, aresistance element and contact means for said resistance element formedintegrally with said condenser plates.

2. A variable grid leak comprising a fixed condenser including oppositecondenser plates and a grid leak resistor including a movable resistanceelement and stationary contact means, in electrical engagen'lent withthe movable resistance element, said stationary contact means being madeintegral with the plates of the condenser by forming a contact means anda condenser plate in the same blank of sheet material.

3. A variable grid leak comprising a condenser and a grid leak resistorincluding a movable resistance element having concentrically connectedlines of a high resistance material, and stationary contact means associated therewith, said stationary contact means being integral with theplates of the condenser by forming a contact means and a condenser platefrom the same blank of sheet material. v

4. Avariable grid leak comprising a condenser including opposite plates,a grid leak resistor including a movable resistance element havingconcentrically connected lines of a high resistance material, and aplurality of stationary contact arms associated therewith, said contactarms being integral with the opposite plates of the condenser, and gridleak terminals also integral with the plates of the condenser, acondenser plate, a grid leak terminal and a contact arm being formedfrom the same blank of sheet material.

5. A variable grid leak comprising a condenser unit, and Ya variableresistor including stationary contact means connected to the condenserunit ,and a movable resistance unit movable relatively to and inengagement with the contact means the resistance unit being removablymountable on the condenser unit.

denser unit including end plates each provided with an integral contactarm and a variable resistance unit detachably mounted on the condenserunit and movable relatively to and in contact with said contact arms.

7, A variable grid leakcomprising a condenser unit including end plateseach provided with an integral contact arm and a connecting terminal,and a rotatable resistance unit detachably mounted on the condenser unitand movable relatively to and in contact with said contact arms.

8. A new article of manufacture comprising a condenser includingopposite condenser plates, a resistance element, contact arms for theresistance element integral with the condenser plates, and terminalconnecting means integral with the condenser plates, a plate, a contactarm and a terminal being formed from a single blank of sheet matrial,

9. A device of the class described, comprising a supporting plate, acondenser mounted thereon having opposed apertured plates, and avariable resistor in circuit with the condenser and provided with anoperat ing spindle extending through the apertures oi the condenserplates and through the supporting plate.

10. A device of the class described, comprising asupporting platemountable on a panel, a condenser mounted thereon having opposedcentrally apertured plates, and a variable resistor in circuit with the0011- ing plate, the said plate forming an. electroe static shield forthe condenser and resistor.

11. A device of the class, described, comprising a supporting plate, asleeve thereon,

' spaced insulating blocks on the sleeve, a condenser includingcondenser plates between the blocks and locked thereto, means forretaining the blocks and condenser on the sleeve, and a variableresistor comprising a rotatable resistance element having a shaftreceived by said sleeve.

12. A device of the class described, comprising a plate, a sleevethereon, spaced insulating blocks on the sleeve, a condenser includingcondenser plates between the blocks and locked thereto, means forretaining the blocks and condenser on the sleeve, aresistance elementcomprising an insulating block provided with graphite lines on itsperipheral wall, the said resistance element being provided with anoperating shaft received by the said sleeve, contact arms for thereslstance element integral with the condenser plates, grid leakterminals also integral with 1 a the condenser plates, and a casingenclosing 6. A variable grld leak comprising a conthe condenser andresistor parts.

Signed at New York city in the county of New York and State of New York,this 8th day of March A. D. 1923. r

/ LESTER L. Jones.

